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Thermoelectric Cooler Helps Maintain Curiosity’s Temperature

Saturday, 01 December 2012

The first spectrometer data from the Mars Rover Curiosity
has made its way back to Earth, analyzing the plasma light captured
during laser excitation of rocks and soil on the planet’s
surface. Solid-state thermoelectric technology was used to
cool the ChemCam (Chemistry Camera) CCD sensors.
Maintaining temperature is critical for successful operation,
and the Thermoelectric Assembly (TEA) provided a reliable
cooling solution.

Marlow Industries designed and built a custom TEA for the
Rover’s ChemCam. Together with NASA’s Jet Propulsion
Laboratory, they developed an assembly that included three
thermoelectric modules (TEMs), one for each CCD in the
ChemCam, and a mounting configuration that located the
assembly inside the instrument’s body.

The TEMs are two-stage, semiconductor-
based devices that function as small
heat pumps. Their cooling-mode operation
is based on the Peltier effect. Driven
by DC power, they pre-cool the CCD
before the lasers fire, and maintain a
constant temperature across the 1024 x
1024 pixel CCD while the laser is firing.

Thermal sensors on or near the CCDs
provide continual feedback to the TEMs’
electrical power input. A feedback loop
keeps the temperature at 0 °C. If the temperature
outside warms up and the CCD
temperature starts to rise above this target,
the controls provide more power to
the coolers, driving them to cool. The
TEMs move heat from the detectors into
the ChemCam body via conduction. The
heat’s thermal path travels through the
frame to the chassis of the rover.

TEMs offer a unique way to provide
cooling for this mission. They not only
offer the ability to meet the mission’s
thermal requirements, but do so within
the project’s limited power, electrical,
and physical space constraints. Without
requiring special accommodations,
TEMs offer rugged cooling capacity that
can withstand the high-vacuum environment
during the cruise to Mars, and last
during operation in the Martian atmosphere.
Since TEMs are solid-state
devices with no moving parts, they can
withstand the mechanical shock, vibration,
and acceleration requirements
during the critical moments from a
mechanical loading standpoint launching
from Earth and deploying on Mars.
They also provide reliable operation as
Curiosity moves around on the planet,
offering the ability to complete potentially
thousands of tests over the twoyear
mission.

On Mars, the ChemCam will primarily
gather samples during the day, and the
TEA is designed for daytime operation.
The worst-case operating condition for
the TEA’s cooling mode is a hot environment
during the Martian summer at its
equator. Even in these extreme conditions,
temperatures will remain under
27 °C, far below the space qualification
temperatures for TEAs that range up to
85 °C.

Thermoelectric solutions are designed to operate in Argon, Xenon, or
Nitrogen backfilled environments, in
both high- and no-vacuum atmospheres.
While each gas and environmental condition
results in different heat conduction
and convection effects, the expected
environments on Mars did not create
a design impediment.

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